COVID-19 outbreak brought about many challenges including the shifting of university assessments to conduct in online mode. This research study tries to explore the impact of newly designed online formative assessments on students' learning, in a Plant Physiology course. The designing of assessments were carried out focusing on constructive alignment, for which an Open Book Test (OBT) was conducted in three parts: OBT1-problem based learning assignment, providing feedback using a rubric; OBT2-multiple choice, multi response, matching and missing word questions with immediate feedback; OBT3-analysing research results with MCQs and short answer questions with feedback. A mixed approach of convergent parallel design method was followed to collect data through two questionnaires and interviews. Findings indicated students' engagement in self- determined learning in solving a real-world problem and their enthusiasm in learning with research-based questions in assessments, while self-assessing their performance through feedback. However, geographically varied technological challenges need to be addressed in conducting successful online assessments.